Arthur greets the strange rider, inviting him to stay. The knight says he has not come to visit, but to test Arthur's knights, who are famed as the best on earth. He asks instead for a Christmas game: He will trade a blow for a blow. If any man is brave enough to strike the Green Knight with his ax, he will give that man the ax to keep. However, that man must agree to receive the same stroke back in a year's time. The knights do not respond, and the green rider jeers at them. Angered, Arthur accepts the challenge and takes the ax, but Gawain asks to be given the task, saying that it is unseemly for the king to do it. Arthur gives him the ax. The Green Knight reminds Gawain of the terms of their agreement. The knight kneels down, and Gawain chops off his head. The Green Knight picks up his head and gets back on his horse. He tells Gawain to look for the Green Chapel, and then rides out of the hall. Arthur masks his amazement by saying that the event was an entertaining interlude. They hang the ax on the wall and continue the feast.

Analysis

The knight's challenge of a blow for a blow draws on a well-known motif from Celtic legend. Two versions of the "beheading game" appear, for example, in "Briucriu's Feast," a tale of the Irish hero Cuchulainn. In the most important of the two, usually called the "Champions' Bargain," an uncouth giant comes into the hall and challenges one of the heroes to chop off his head that night, if he can then chop off the hero's tomorrow. After one agrees, the giant picks up his head and walks away. The hero stays away the next day, as do several others, but Cuchulainn keeps his end of the bargain, and the giant responds by striking him with the blunt side of the ax, so that Cuchulainn is not harmed. Similar beheading challenges occur in Arthurian literature as well, specifically the French romances LeLivre de Caradoc and Perlesvaus. The year's delay for the exchange also has Celtic precedent. In the Welsh legend "Pwyll," found in the Mabinogion, Pwyll has to pay a debt to the hunter Arawn, the king of the underworld, for Pwyll's discourtesy during a hunt. Arawn and Pwyll magically swap appearances and take each other's places for a year and one day. Although relying on Celtic and French source material, the Gawain-poet does not simply rehash it. Instead, in the best medieval fashion, he appropriates it for his own purposes, subtly altering it to give it a new context and meaning.

The Green Knight is brash and a little rude in proposing his game. When Arthur's knights — understandably puzzled by this bizarre creature's offer to let someone cut off his head — do not respond to the challenge, the Green Knight rolls his eyes and laughs, mocking them as cowards. In contrast, when Gawain finally speaks up, he is all politeness and modesty. His elaborate speech is strenuously deferential, as he humbly asks permission even to leave Guenevere's side. He takes pains not to call attention to himself or to seem vain in taking the challenge away from Arthur, protesting that so foolish a matter should fall upon the weakest and most foolish member of the court. Arthur's nephew Gawain is in fact one of the strongest and bravest at the feast, but here we see him living up to his legendary reputation as the most courteous of Arthur's knights. "Courtesy," in a knight's code of behavior, meant much more than simple politeness, being closely related to the values of chivalry and courtly love. It included sincere humility, gracious manners, kindness, and respectful treatment of others, even those below one's social station, and especially women. Gawain's acceptance of Arthur's task also makes him effectively the representative of Camelot and the Arthurian ideal itself.

The poem makes constant reference to games, laughter, and entertainments, and nearly all the action takes places at the holidays, when gifts are exchanged. The Green Knight insists that he has not come to fight but to play a game, and a Christmas game at that. Yet if you compare this game to the light-hearted kissing games the court had been playing earlier in the day, the stakes seem frighteningly high. It soon becomes clear to the court that Gawain will have to give up his life rather than just a few kisses — although kisses will figure again in the game before it ends. If the beheading really is a game, perhaps the Green Knight's challenge is actually a kind of exchange of gifts. The Green Knight's insistence that Gawain rehearse the terms of their agreement, within the hearing of the entire court, sets the rules of the game. But these rules also sound like the terms of a legal contract, in which goods or services are exchanged under mutually agreed circumstances. Gawain's and the reader's understanding of the rules is unfortunately incomplete, and the Green Knight offers no help: Even though he promises to tell Gawain his name and where to find him, he says only to look for the Green Chapel, without indicating where that might be. Fairy tales and folk tales often involve impossible conditions and mysterious requirements imposed on the hero, and Sir Gawain and the Green Knight has many elements that recall fairy tales — for example, the tendency for events to occur in threes, as will happen when Gawain actually finds the Green Knight.

Why the Green Knight's weapon is an ax, not a sword, has been a subject of speculation. The weapon in "Briucriu's Feast" is also an ax, so the poet may simply be sticking to his source material. An ax can be a woodsman's tool as well as a weapon of war, and this may reinforce the Green Knight's association with the forest. An ax can also be an executioner's instrument, leading some critics to see the Green Knight as a personification of Death itself. Other critics have seen a Biblical source for the ax, Matthew 3:10, with its dire spiritual warning, "The ax is already at the root of the trees, and every tree that does not produce good fruit will be cut down and thrown into the fire." Nonetheless, the Green Knight insists that he comes in peace, as evidenced by his lack of armor and the fact that he carries a green branch (a sprig of Christmas holly, instead of an olive branch) as a token of peace.

Arthur's final reaction to the episode has provoked multiple interpretations. The poet says Arthur is amazed, but publicly, he masks his amazement by calling the event an "interlude" or entertainment appropriate to a grand feast. In fact, feasts at a royal court commonly included staged interludes between the courses, in which strangely costumed "visitors" might enter the hall to entertain the guests. But for his green skin, the Green Knight could be an actor in one of these interludes. Perhaps Arthur is trying to hide his fear or pass off the event as a fake, or perhaps he is simply to trying to reassure his shaken guests by showing no outward concern over the incident. In the end, he tells Gawain to hang up his ax, which is a proverbial phrase for stopping one's work, because for the moment, the game is ended.